The present invention relates to a method and apparatus for testing flexible pipes. In particular, but not exclusively, the present invention relates to a method of applying a conditioning and/or test cycle to a flexible pipe and simultaneously applying the same cycle to a specimen connected in an in-line configuration with the flexible pipe. The specimen includes one or more layers previously removed from the body of the flexible pipe and can subsequently be disconnected from the pipe. The layers in the specimen can then be analysed to determine any potential effect of the conditioning or testing on the flexible pipe (which itself remains intact).
Traditionally flexible pipe has been utilised to transport production fluids, such as oil and/or gas and/or water from one location to another. Flexible pipe has been found to be useful in connecting a sub-sea location to a sea-level location. Flexible pipe has generally been formed as an assembly of flexible pipe body and one or more end fittings. The pipe body is conventionally formed as a combination of layered materials that form a pressure-containing conduit. The pipe structure allows large deflections in use without causing bending stresses that impair the pipe's functionality over its lifetime. The pipe body is generally built up as a combined structure including tubular metallic and polymer layers which are typically unbonded.
Such unbonded flexible pipes have been used for deep water (less than 3300 feet (1005.84 meters)) and ultra-deep water (greater than 3300 feet (1005.84 meters)) developments. Of course flexible pipe may also be used for shallow water applications (for example, less than around 500 meters depth) or even for on-shore (overland) applications.
Flexible pipes often incorporate one or more polymer layers, such as PVDF (polyvinylidene fluoride) that may be formed by extrusion. Most polymers have a certain maximum allowable strain above which the risk of damage to the material is much greater. In flexible pipes where a polymer layer lies adjacent an armour layer (such as a polymer barrier layer located adjacent a metallic pressure armour layer), the polymer layer may be subjected to quite severe non-uniform, highly localised strain. This is because an armour layer is usually formed from interlocking wires of certain cross-section and there are certain gaps between adjacent windings. The polymer layer tends to deform and creep into those gaps when under pressure.
The application of internal pressure to the pipe (i.e. which can occur when an inner bore is pressurised) produces radial expansion in all layers and under such circumstances a polymer may undergo deformation and tend to creep into gaps of an overlying armour layer. At high pressures (for example, about around 8000 psi/55 MPa or more), the resultant strain distribution within the polymer can be highly localised at the areas around the gaps and the polymer material may deform by cavitation rather than plastic flow. This can in turn result in the formation of micro-crazing or micro-cracking on the radially inner surface of the polymer layer. During any subsequent loading (such as the loading experienced during normal use in transporting production fluids) this micro-crazing may then extend to form longer/deeper cracks throughout the polymer layer. This increases the risk of failure of the polymer layer and may ultimately lead to loss of pressure containment having an adverse effect on the lifetime of a flexible pipe.
In order to ensure there is little or no risk of such micro-crazing or micro-cracking and in accordance with industry regulations, all flexible pipe structures must undergo a factory acceptance test (FAT) subsequent to manufacture and prior to delivery. This involves pressurising a manufactured pipe bore with a fluid, such as water, at 1.5 times the usual pressure expected during use. The water is thus a pressurising medium. The FAT is required by industry standards to be 1.5 times the design pressure of the pipe and this pressure is typically maintained for a minimum of 24 hours. This is typically the highest and most severe pressure cycle that any flexible pipe will ever experience in its lifetime. A successful subsequent evaluation identifying no crazing on a test sample from the same production run experiencing the same pressure cycle thus gives evidence to a potential client that a flexible pipe itself has been manufactured in an acceptable manner. Conventionally such testing has been carried out on a flexible pipe and then parts of the flexible pipe cut through destructively and subsequently analysed. This is a time consuming and costly process since a flexible pipe must first be manufactured including terminating ends of pipe body with end fittings. At least one of these end fittings must then be removed to provide access to part of the pipe which can be removed and used as a test sample. The remainder flexible pipe body and end fitting must then be re-sealed with a new end fitting. Apart from being a time consuming and costly process this is also prone to error and the resultant flexible pipe is not exactly the same as that tested.
It is an aim of the present invention to at least partly mitigate the above-mentioned problems.
It is an aim of certain embodiments of the present invention to provide an in-line test method in which a test piece including one or more tubular test layers can be provided in an in-line configuration with a flexible pipe.
It is an aim of certain embodiments of the present invention to provide an-line conditioning method in which a conditioning piece including one or more tubular conditioning layers can be provided in an in-line configuration with a flexible pipe.
It is an aim of certain embodiments of the present invention to provide a method and apparatus for probing a layer of a flexible pipe. That is to say, applying a conditioning cycle and/or a test cycle to a flexible pipe and specimen connected in an in-line configuration with the flexible pipe simultaneously.
It is an aim of certain embodiments of the present invention to enable a flexible pipe to be manufactured and tested intact without subsequently having to destroy part or parts of the flexible pipe and thereafter re-fit an end fitting.
It is an aim of certain embodiments of the present invention to provide apparatus for testing a non-metallic layer used in flexible pipe body.